If you take my advice and visit the Yumenoshima Tropical Greenhouse Dome, an excellent botanical garden with tons of exotic flowers, you might also want to stop in at the Daigo Fukuryu Maru Exhibition Hall.
I chanced upon it while exploring the park that the botanical garden is in, and popped my head in the door wondering why there was a big wooden boat on land in the park. I took a couple of photos, and was about to leave because I though it was just a museum about tuna fishing.
Then I noticed the pictures of the sailors with radiation burns and the paper cranes. It turns out that the place is a monument to a tragic nuclear accident that happened in the 1950s. When America was testing the hydrogen bomb in the Bikini Islands in 1954, they underestimated the power of the bomb, which turned out to be twice as powerful as they thought. The boat entered the fallout area, and all 23 of its crew members were exposed to high levels of radiation.
There’s more information about the incident at: http://en.wikipedia.org/wiki/Daigo_Fukury%C5%AB_Maru
It’s quite a small museum that you can see in a few minutes. There are some English translations of newspaper articles about the incident, so it’s pretty easy to understand. Admission is free.
There’s a map of the park and access information at: http://www.kensetsu.metro.tokyo.jp/kouen/kouenannai/park/english/yumenoshima.pdf
Marina nearby the Daigo Fukuryu Maru Museum.